Download Alternate Pathways of Respiration

Related Pathways of
Cellular Respiration
AKA…
Not the hard part. In fact, if you
know the normal path, this should
be easy.
Alternate Fuels

Carbs are the first choice. What if we don’t eat carbs?
Proteins
 Proteins are the third choice of energy – after carbs and
lipids.
 Amino acids undergo deamination in which the amino
groups (-NH2) are removed and made into ammonia.
 The remainder of the amino acid is converted into an
intermediary of glycolysis or the Kreb’s cycle depending
on the identity (R-group) of the amino acid.
Fat Fuel
Lipids
Lipids are the second choice for the body (despite the
fact they hold more energy per unit than any carb).
 Triglycerides are the main fat in food – they are broken
down into fatty acids and glycerol.
 Glycerol may go through gluconeogenesis and be
converted into glucose or enter glycolysis as one of the
3-carbon intermediaries.
 Fatty acids undergo ß-oxidation in which they are cut
into 2-carbon pieces that enter the Kreb’s cycle as
Acteyl-CoA’s. (Do the math – its huge!)

Anaerobic Pathways
The term “anaerobic” means “in the absence of
oxygen”.
 There are many methods of anaerobic
respiration but eukaryotes mostly use just two
methods of anaerobic respiration – ethanol
fermentation and lactate (lactic acid)
fermentation. Fermentation means the process
is anaerobic.
 Both processes will use glycolysis to start as it
does not require oxygen. The difference will be
what we do with the pyruvate at the end of
glycolysis.

Why Ferment?
Glycolysis occurs first and gives a small yield of
ATP but in the process you use up some NAD+.
Without the ETC being used because it is
aerobic, the NADH’s stay as NADH’s and all of
the NAD+ gets used up and you can't even run
glycolysis after a while.
 You have to have a way to recycle your NAD+
and NADH or you won’t even be able to get the
little bit of energy glycolysis offers. That is why
things run fermentation.
 It’s not a lot of energy but it is way better than
no energy!

Ethanol Fermentation


Ethanol fermentation is an anaerobic respiration process
carried out by yeast cells – they can run fermentation and
survive just fine because yeast cells do not require a lot of
energy – they are boring!
So here is what happens…
1.
2.
3.
Glycolysis: Glucose  2 Pyruvate
2 Pyruvate  2 Acetaldehyde + 2 CO2
2 Acetaldehyde  2 Ethanol

During this, we get the recycling of NAD+ and NADH.

Ethanol fermentation is used in bread, beer and wine
making.
Ethanol Fermentation
Lactate Fermentation
Lactate fermentation occurs in animals like us
humans when we exert high physical demands
on our body
 Our cell’s energy needs exceed our body’s ability
to supply oxygen – we can’t breathe fast enough
so the cells have to use something other than
oxygen.
 We use lactate fermentation but can’t do so for
long because glycolysis does not give enough
ATP to keep us going. We need a lot of ATP!

Lactate/Lactic Acid Fermentation

So what do we do when we can’t breathe fast
enough?...
1.
2.
Glycolysis: Glucose  2 Pyruvate
2 Pyruvate 2 Lactate

The NAD+ and NADH are recycled during this process.

After the strenuous activity – we still breath hard to
repay the oxygen debt. The oxygen goes back in to
catabolize the lactate to CO2 and H2O.
We use lactic acid fermentation when we want to build
muscle – feel the burn!

Lactate/Lactic Acid Fermentation
FIN
(Yeah, you may have worked hard, but
not hard enough to feel the burn.)